GB2026093A

GB2026093A - Jet pump nozzle construction

Info

Publication number: GB2026093A
Application number: GB7923205A
Authority: GB
Original assignee: Dresser Industries Inc
Current assignee: Dresser Industries Inc
Priority date: 1978-07-12
Filing date: 1979-07-04
Publication date: 1980-01-30
Also published as: FR2432632A1

Abstract

A mixing and diffusing nozzle for an oil well jet pump comprises a smooth inlet 44, a mixing section 46 of constant diameter, a frustoconical prediffuser 48, and a frustoconical diffuser 50. The angle of divergence of the diffuser 50 is substantially greater, preferably twice as great, as the angle of divergence of the prediffuser 48. The prediffuser diverges at a rate approximately equal to the rate of increase in thickness of the fluid boundary layer in the prediffuser whereby the constraining effect of the boundary layer is reduced. <IMAGE>

Description

SPECIFICATION Jet pump nozzle construction This invention relates to jet pump constructions. More specifically the invention is related to a specific improvement in the nozzle configuration of a jet pump suitable for downhole oil well service.

Prior art nozzle configurations for downhole oil well jet jumps utilize a simple nozzle construction which has the outlet of a fluid power nozzle directed into the inlet of a classically simple second nozzle which mixes fluid from the power nozzle with well fluid and discharges the combined fluids to the pump outlet. The mixing and diffusing nozzle typically has a reduced diameter throat which is slightly larger than the outlet of the power fluid nozzle and is followed by a divergent conically shaped section to communicate the fluid to the pump outlet. Typically the mixing and diffusing nozzle is relatively long compared with the throat diameter.Because of this elongate configuration, a substantial thickness of fluid builds up in a boundary layer around the interior of the nozzle along the surfaces of the walls thereof which is well known in the art to reduce the effective diameter of the conduit. Because of this boundary layer build-up the internal diameter of the nozzle is effectively reduced by the thickness of the boundary layer so the overall result is that a smaller volume of fluid will flow through the jet pump for a given pressure differential across the pump.

According to one feature of the present invention there is provided a mixing and diffusing nozzle for a jet pump, the nozzle including: an inlet having a smoothly contoured annular opening and joining the inlet end of a mixing conduit which extends downstream in the fluid flow path therefrom; a frustoconically shaped prediffuser conduit joining said mixing conduit and extending downstream therefrom, said prediffuser having a longitudinally elongate divergent form with the small diameter portion thereof joining said mixing conduit; and, a diffuser conduit joining said prediffuser downstream thereof and having an elongate divergent form with the small diameter portion thereof connecting to said prediffuser, said diffuser being divergent at a larger rate than said prediffuser relative to downstream fluid flow.

The invention will be better understood from the following description of a preferred embodiment thereof, given by V ay of example only, reference being had to the accompanying drawings, wherein: Figure 1 is a cutaway elevation view of a portion of a downhole oil well jet pump positioned in the earth supported casing of an oil well; Figure 2 is an enlarged cross-sectional elevation view of portions of the nozzle assemblies from a downhole oil well jet pump shown in Fig. 1 with the fluid boundary layer shown on one side of the nozzle; and Figure 3 is a graph of pump pressure ratio and pump efficiency versus mass flow ratio for a jet pump using the nozzle construction of this invention.

Fig. 1 of the drawings illustrates in cutaway view a portion of a downhole oil well jet pump in place within a section of well casing.

The jet pump, indicated generally at 10, is suspended by a length of tubing 1 2 which hangs from the well head at the surface or ground level. The well casing 1 4 is rigidly mounted in the ground 1 6. At the lower end portion of the jet pump, a seal assembly (not shown) separates a well fluid chamber below the pump inside the well casing from a pumped fluid chamber 1 8 surrounding the jet pump within the well casing. Power fluid for the jet pump is forced downward through tubing 1 2 where it is mixed in the pump with well fluid that enters the pump from below. In the lower portion of pump housing 34, a well fluid inlet check-valve, indicated generally at 20, is provided to accommodate the entrance of well fluid into the pump.Along the flow path of the well fluid into the pump a checkvalve, indicated generally at 22, is provided at the entrance to a pump internal well fluid chamber 24.

A power fluid nozzle 26 is mounted within internal well fluid chamber 24 and receives power fluid through a series of internal passageways within the jet pump. Power fluid nozzle 26 is formed on one end of an enclosure 28 that is positioned within internal well fluid chamber 24 and supported from the wall 30 thereof. The interior of enclosure 28 is provided with a plurality of apertures through wall 30 to establish fluid communication with a power fluid chamber 32 around the exterior of wall 30. Power fluid chamber 32 is formed between the exterior of wall 30 and the interior of the pump housing or casing 34.

Power fluid chamber 32 is in fluid communication with the outlet of a power fluid inlet checkvalve, inciated generally at 36, mounted in the upper portion of the pump and receiving the power fluid from tubing 1 2. The mixing and diffusing nozzle of the jet pump is indicated generally at 38 and positioned physically above or downstream of power fluid nozzle 26. Mixing and diffusing nozzle 38 receives the well fluid from internal well fluid chamber 24 and the power fluid exiting from power fluid nozzle 26 and mixes both fluids and displaces them to a pumped fluid outlet 40. From pumped fluid outlet 40 the fluid flows into annular pumped fluid chamber 1 8 between the exterior of the jet pump and tubing 12, and within well casing 14 so the pumped fluid can travel to the surface of the well.

Fig. 2 shows an enlarged detailed construction of the outlet portion of power fluid nozzle 26 and the major portion of mixing and diffusing nozzle 38. Fluid is guided into the entrance of mixing and diffusing nozzle 38 by a smoothly contoured inlet 44 spaced a short distance from the discharge end of power fluid nozzle 26 so that power fluid can flow directly into mixing nozzle 38 and also cause the well fluid in internal well chamber 24 to be drawn into the mixing nozzle. The initial interior portion of nozzle 38 immediately downstream of inlet 44 is a mixing conduit segment 46 which extends through the nozzle a length indicated by LM. Immediately downstream of mixing conduit 46 is a prediffuser 48 which extends through the nozzle a length LP.Prediffuser 48 precedes a conventional nozzle diffuser 50 which extends from the termination of prediffuser 48 to a chamber at the end of the fluid passageway within the pump immediately preceding the pumped fluid outlet 40.

Mixing conduit 46, in the configuration shown, is a cross-sectionally circular and substantially constant diameter conduit segment which begins at the smallest radial diameter portion of inlet 44 and extends to a midportion of the nozzle where it joins prediffuser 48. Prediffuser 48 is, in the configuration shown, a substantially cross-sectionally circularly and uniformly divergent conduit segment which begins at the termination of mixing conduit 46 and extends to a further downstream mid-portion of the nozzle where it joins diffuser 50. Diffuser 50 is a substantially cross-sectionally circular and uniformly divergent conduit segment which extends from the termination of prediffuser 48 to the most downstream end of the nozzle. Diffuser 50 is divergent at a greater rate than prediffuser 48 relative to fluid motion along the downstream flow path of the nozzle from the inlet thereof.

Prediffuser 48 and diffuser 50 are shaped substantially like the frustom of a cone.

Prediffuser 48 is constructed with sides thereof divergent at a uniform angle as indicated at A measured between the sides of the conduit. Angle A can vary between approximately 1 1 /2 degrees to approximately 4 1/2 degrees. The divergent angle of diffuser 50 is indicated at B. Angle B can vary from approximately 3 degrees to approximately 9 degrees. In practicing the invention, a pump has been constructed and successfully tested with angle A being around approximately 3 degrees and angle B being around approximately 6 degrees. Mixing conduit 46 is preferably shorter than prediffuser conduit 48.

The combined length of mixing conduit 46 and prediffuser 48 is substantially less than the length of diffuser 50. Obviously, the specific and relative lengths of the various sections of the nozzle can be selected at the designers option depending upon the specific design criteria involved without departing from the scope of the invention.

When the jet pump is in operation, the normal flow of fluid through nozzle 38 causes the formation of a boundary layer of fluid to be formed along the walls of the nozzle as is well known in the art of fluid mechanics. This boundary layer is indicated in Fig. 2 at T. The boundary layer is infinitesimally thin at the beginning of fluid flow through the nozzle at inlet 44 and increases in thickness at a predeterminable continuing rate throughout the length of the nozzle. Because of the accumulated thickness of this boundary layer of fluid around the interior of mixing conduit 46, it will normally create a restricted flow through this portion of the nozzle for any substantially extended length of mixing conduit.Prediffuser 48 alleviates this restriction by providing a slightly divergent section of conduit prior to diffuser 50 which allows the fluids to continue mixing without significant diffusion. Prediffuser 48 is sufficiently divergent to accommodate the boundary layer build-up or thickness T at any point along its length so that the effective cross-sectional area of the nozzle through which the fluid is flowing is not effectively diminished. This function of prediffuser 48 permits continued mixing of the fluids and in effect provides an extended mixing conduit ahead of the diffuser section of the nozzle. Mixing conduit 46 and prediffuser 48 function cooperatively as an elongated divergent mixing conduit or a two stage mixing nozzle.Once the fluid enters diffuser 50 from prediffuser 48, the boundary layer of course continues to increase in thickness; however, this increase in thickness is more than compensated for by increasing divergence of diffuser 50.

In regard to the specific nozzle construction, the mixing conduit length LM can be shorter than the prediffuser length LP without significantly effecting the fluid flow. The boundary layer thickness T is a function of a the pressure gradient in the mixing conduit and the length of the mixing conduit. Thus, because of the short mixing conduit a substantial increase in boundary layer thickness does not usually occur. The prediffuser angle A can be the above noted angle of approximately 3 degrees for the size of nozzle construction and fluids normally encountered in downhole oil well jet pumps.

As noted above, a pump utilizing the jet pump nozzle configuration of this invention has been made and successsfully tested. In this test pump, a significant increase in overall pump efficiency and the pump pressure ratio has been noted. Graphical illustration of this data is shown in Fig. 3 where the performance of a pump having a 6 degree diffuser angle and without the prediffuser is compared with a substantially similar pump that has the prediffuser.

In testing of the pumps, several physical measurements were taken of each pump operating in the same test apparatus. Calculations of the data for the curves shown in Fig. 3 were made from the following: Pump pressure ratio Pd - PF N= Pj Pd Where Pd = discharge total pressure PF = formation total pressure Pj = jet total pressure Mass flow ratio QFWF Q= QjWj Where QFWF = formation fluid mass flow rate = = jet or power fluid mass flow rate Pump efficiency n = NxQ In the test facility, the formation total pressure was created by placing the pump in a pressurized fluid chamber. Also, pressures and flow rates were monitored at appropriate locations in the test facility to provide the appropriate data.For the data shown in Fig. 3, P- = 2,000 pounds per square inch and PF = 500 pounds per square inch.

In comparing the pump pressure ratio curves "N" in the upper portion of the graph, it can be observed that the nozzle with the prediffuser has a consistently higher value for any given flow rate than does the nozzle without the prediffuser. Considering the increase in effective flow area through the nozzle provided by the prediffuser, it can be anticipated that Pd would also be larger therefore resulting in a larger N (pump pressure ratio) for a given Q (mass flow ratio) considering all other things substantially equal.

In regard to the pump efficiency (n), this is a direct function of the pump pressure ratio (N) and the mass flow ratio. Therefore, for a given flow rate the pump with the prediffuser will have a higher efficiency because of the consistently higher pressure ratio.

As a result of this higher efficiency in a field situation, an oil well jet pump having the prediffuser will lift the same amount of fluid from a well as a jet pump without the prediffuser but a lower horsepower input will be required into the pump through the power fluid.

As will become apparent from the foregoing description of the applicant's invention, a relatively simple yet extremely effective two stage nozzle construction has been provided which will increase the operating efficiency of the pump.. The addition of the prediffuser in the nozzle reduces the resistance of fluid to flow through the mixing segment of the nozzle thereby effectively reducing the back pressure of the nozzle as seen by the fluid power source which is operating the pump. This decrease in back pressure as seen by the fluid power source as compared with a conventional nozzle construction can be considered as increased efficiency attributable to this novel pump nozzle design.

Claims

1. A mixing and diffusing nozzle for a jet pump, the nozzle including: an inlet having a smoothly contoured annular opening and joining the inlet end of a mixing conduit which extends downstream in the fluid flow path therefrom; a frustoconically shaped prediffuser conduit joining said mixing conduit and extending downstream therefrom, said prediffuser having a longitudinally elongate divergent form with the small diameter portion thereof joining said mixing conduit; and, a diffuser conduit joining said prediffuser downstream thereof and having an elongate divergent form with the small diameter portion thereof connecting to said prediffuser, said diffuser being divergent at a larger rate than said prediffuser relative to downstream fluid flow.

2. A mixing and diffusing nozzle according to claim 1 wherein the mixing conduit has a substantially constant diameter.

3. A mixing and diffusing nozzle according to claim 1 or claim 2 wherein the prediffuser conduit and the diffuser conduit are crosssectionally round.

4. A mixing and diffusing nozzle according to any preceding claim, wherein said prediffuser is divergent an amount at least equivalent to the thickness of any fluid boundary layer occurring downstream of the inlet to said prediffuser at any point along the longitudinal flow path within said nozzle; and said diffuser is divergent at a rate substantially greater than the divergent rate of said prediffuser.

5. A mixing and diffusing nozzle according to any of claims 1 to 3, wherein the prediffuser conduit segment is divergent at a rate approximately equal to the increasing thickness of the fluid boundary layer which is built up within the prediffuser during normal operation of said jet pump.

6. A mixing and diffusing nozzle according to any preceding claim, wherein said prediffuser is frustoconically shaped and divergent at an angle of between approximately 3/4 to approximately 2 1/4 degrees on each side thereof relative to the longitudinal axis of said mixing conduit.

7. A mixing and diffusing nozzle according to claim 6, wherein said diffuser is frustoconically shaped and divergent at an angle of between approximately 1 1/2 to approxi mately 4 1/2 degrees on each side thereof relative to the said longitudinal axis.

8. A mixing and diffusing nozzle according to any of claims 1 to 5, wherein said elongate mixing conduit is cross-sectionally circular; said prediffuser is frustoconically shaped and divergent at an angle of about 3 degrees between opposed sides thereof; and said diffuser is frustoconically shaped and divergent at an angle of about 6 degrees between opposed sides thereof.

9. A mixing and diffusing nozzle according to any preceding claim, wherein said prediffuser is substantially longer than said mixing conduit and said diffuser is substantially longer than said prediffuser and said mixing conduit together.

10. A mixing and diffusing nozzle according to any preceding claim, wherein said prediffuser is divergent at an angle less than the divergent angle of said diffuser.

11. A mixing and diffusing nozzle according to any preceding claim wherein said prediffuser and said diffuser are each cross-sectionally circular transverse to the elongate axis of said nozzle and divergent at a uniform rate from the respective smaller diameter end portion thereof.

12. A mixing and diffusing nozzle for a jet pump, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

1 3. A jet pump having a first inlet for pumped fluid; a second inlet for power fluid; an outlet for pumped fluid; and a power fluid nozzle directed into the inlet of a mixing and diffusing nozzle, the mixing and diffusing nozzle also receiving pumped fluid in the inlet thereof to mix with the power fluid and direct both of them to the pump outlet, the mixing and diffusing nozzle being a nozzle according to any preceding claim.

14. A downhole oil well jet pump having an inlet for well fluid, a second inlet for power fluid, an outlet for pumped fluid, and a power fluid nozzle directed into the inlet of a mixing nozzle, the mixing nozzle also receiving well fluid in the inlet thereof to mix with the power fluid and direct both of them to the pump outlet, the mixing nozzle comprising: a smoothly contoured inlet at the entrance of the mixing nozzle; a contant diameter mixing conduit immediately downstream of the inlet wherein said power fluid and said well fluid are initially mixed as they flow downstream within the mixing nozzle; a frustoconically shaped prediffusing conduit segment immediately downstream of said constant diameter mixing conduit and extending downstream therefrom wherein further mixing of said well fluid and said power fluid takes place and the constraining effect of boundary layer fluid build-up are reduced prior to diffusing of the fluids; and a frustoconically shaped diffuser conduit segment immediately downstream of said prediffuser conduit segment and extending further downstream therefrom, said diffuser having a greater divergence of the sides thereof than said prediffuser such that diffusion of the fluid takes place prior to entering the pump outlet.

1 5. A jet pump, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.